1. Field of the Invention
Embodiments of the present invention relate to a semiconductor device and a method for forming the same, and more particularly to a semiconductor device including a contact plug and a method for forming the same.
2. Background of the Invention
In a manufacturing process of a semiconductor device, it is necessary to form a metal contact plug for electrically coupling a predetermined lower metal line to an upper metal line. However, in recent times, as the semiconductor device is highly integrated and super-miniaturized, it is necessary to more precisely form a metal contact plug for interconnection between metal lines. In addition, as the demand of electrical characteristics and operation speed of the semiconductor device are further increased, a metal contact plug is required to have a more precise structure, lower resistance, and higher reliability.
Generally, although tungsten (W) and aluminum (Al) are basically used to form a metal line and a metal contact plug, the tungsten (W) and the aluminum (Al) may encounter problems caused by electro-migration or stress-migration. In order to solve the problem, a new method for replacing tungsten (W) or aluminum (Al) with copper (Cu) has been proposed.
Copper (Cu) is generally used as a metal line to increase the operating speed of the semiconductor device. Since copper has difficulty in an etching process, the copper (Cu) is formed using a dual damascene process. In the dual damascene process, an etch stop layer and an interlayer insulating layer are laminated in the form of multiple layers and are etched to form a contact hole and a trench, such that a diffusion barrier and a seed layer are formed over the entire structure including the contact hole and the trench. Subsequently, a copper (Cu) line is deposited by an electroplating process and is polished by a chemical mechanical polishing (CMP) process, such that the contact plug and the copper (Cu) line can be simultaneously formed by the dual damascene process.
As the semiconductor device is highly integrated, the difficulty in forming a minute content hole is also increasing. Although a minute contact hole can be properly formed, its contact resistance is increased due to a shortened distance between the neighboring metal lines. As a result, a defect due to high resistance may occur in the semiconductor device, which makes it difficult for the dual damascene process to be applied for a low-power semiconductor device. Further, when the dual damascene process is applied to the manufacturing process of the semiconductor device with a narrowly scaled down contact hole, it is probable that the contact hole is not fully filled up by conductive material and thus creates a void in the contact plug.
If copper (Cu) fills up the contact hole, copper atoms may diffuse into an neighboring device element to cause contamination. In order to prevent the other device elements from being contaminated, a barrier metal layer is generally formed over the surface of the contact hole. However, due to miniaturization, the barrier metal layer cannot be formed thick enough to prevent copper migration.